Polyimides are widely used in the electronic packaging industry because of their high glass transition temperature, excellent thermal and hydrolytic stability, and chemical resistance. Most polyimides are prepared by a two-step process in which a diamine is condensed with a dianhydride to form a polyamic acid, which is dehydrated to form the polyimide by thermal or chemical methods. Since polyimides are generally insoluble in organic solvents, it is difficult to fabricate electronic package with them. In general, the soluble polyamic acid is coated onto a substrate, and then subjected to high temperatures and long bake times (or chemicals) to complete the imidization process. Such methods are not entirely satisfactory. For example, they hold up the production rate by requiring separate processing steps. In addition, many of the polyimides formed have a thermal coefficient of expansion (TCE) which is not optimum. Also, in these prior art methods, there is a substantial amount of shrinkage. This leads to curling or other manifestation of stress at the coating/substrate interface. For example, in the electronic packaging industry Kapton.TM. resin, a polyimide commercialized by DuPont, is widely used as a dielectric layer. Kapton resin has good resistance to chemical attack, excellent thermal stability (&gt;400.degree. C.), and low dielectric constant. However, Kapton resin is not processible in its imidized form, and consequently it is made available as either an insoluble film or as a soluble precursor, e.g., the polyamic acid in N-methylpyrollidone. Unfortunately, the TCE of Kapton polyimide (35.times.10.sup.-6 /.degree.C.) in the XY plane is larger than the TCE of materials used in the electronics industry such as silicon and copper. The high TCE and high modulus leads to stress at the polymer-metal interface and, therefore, Kapton resin forms materials having less than optimum properties.
For example, stress at the polymer/metal interface can cause curl in coated objects. Curl can be an extremely detrimental problem in devices which must remain substantially flat. For example, in IC chip bonding, if the extent of curl is too high, not all beam leads will become attached to the chip; and consequently the chip may not perform as intended.
Consequently, a need exists for provision of coating materials which have the desirable properties of polyimides, but which substantially obviate the problems (e.g., curl) associated with stress at the resin/metal interface. This invention satisfies that need.